fix(config): print only the value of config get and add display preferences

tea config get printed "key<TAB>value", so $(tea config get editor) was
not usable; it now prints the value alone, and --show-source appends the
source (D18). config get reads the instance's user, and instance settings
come from the selected instance (--host, TEA_HOST, default_host or the
sole instance). Unknown keys list the valid ones, and keys that need
--host or --user say so. config path no longer loads the settings, so it
works when hosts.yml is broken. config list is a table on a terminal.
config set confirms the change on a terminal and warns when default_host
has no account.

config.yml stores the hyperlinks (auto, always, never) and markdown
(auto, raw) preferences that tables and views now read, instead of the
TEA_HYPERLINKS and TEA_MARKDOWN variables. The environment table moves
out of tea config --help into tea help environment.

alias set refuses to replace an alias without --clobber, drops a leading
"tea", and explains how to quote an expansion with spaces or flags.
alias delete takes several names or --all, alias list is a table, and
an empty list says so on a terminal.

Signed-off-by: bircni <bircni@icloud.com>

internal/app/app.go

@@ -279,7 +279,7 @@ func (a *application) checkOutputFlags(cmd *cobra.Command) error {
 
 // offline reports commands that must work without valid settings.
 func offline(cmd *cobra.Command) bool {
-	if cmd.Annotations["tea.group"] == "true" {
+	if cmd.Annotations["tea.group"] == "true" || cmd.Annotations["tea.offline"] == "true" {
 		return true
 	}
 	switch cmd.Name() {
@@ -492,12 +492,6 @@ func commandIndex(root *cobra.Command, args []string) int {
 	return len(args)
 }
 
-// configKeys are the preferences, instance settings and account settings that config get reads.
-var configKeys = []string{
-	"browser", "color", "default_host", "editor", "git_protocol", "insecure", "oauth_client_id", "pager", "prompt",
-	"remote", "ssh_agent", "ssh_certificate_principal", "ssh_host", "ssh_key", "ssh_key_fingerprint", "version",
-}
-
 func commandOutputFields(cmd *cobra.Command) []string {
 	if cmd.Name() == "status" && cmd.Parent() != nil {
 		if cmd.Parent().Name() == "pr" {